A prior example relating to the present invention is disclosed in Japanese Patent Application Laid-Open No. 9-85358, for example. As shown in FIG. 10, in this prior example, a punch driver 205 having a punch head 203 on its upper end is provided to a cylindrical punch guide 201 so as to be movable up and down. A substantially semicircular or substantially triangular blade member 207 having a cutting and protruding blade at its forward end is supported into the punch guide 201 in a position below the punch driver 205 via a pin 209 so as to revolve in a horizontal direction. Moreover, a force is applied to the blade member 207 by a force applying means 211 mounted into the punch guide 201 in a direction where the blade member 207 separates from an upper surface of a workpiece W.
In the above structure, a striker 213 which is provided to the punch press movably up and down strikes the punch head 203 and lowers the punch driver 205 against a stripper spring 215. When a protruded portion 217 provided to a lower end of the punch driver 205 pushes the blade member 207 to a downward direction, the blade member 207 revolves about the pin 209 to the horizontal direction, and the cutting and protruding blade at the forward end of the blade member 207 cuts into the upper surface of the workpiece W supported to a die 219. As a result, the upper surface of the workpiece W is scratched so that a small protrusion 221 is cut and protruded.
In the structure of the prior example, a force is applied to the blade member 207 by the force applying means 211 to the direction where the blade member 207 separates from the workpiece W, and the blade member 207 is mounted into the punch guide 201 via the pin 209 so as to revolve in the horizontal direction. For this reason, it is troublesome to work a pin hole into the punch guide 201 and to assemble the blade member 207 and the like into the punch guide 201. Namely, there arises a problem that the working and assembly of the blade member 207 are troublesome.
In addition, since the protruded portion 217 which is provided to the lower end of the punch driver 205 pushes the blade member 207 directly to the downward direction, a height of a position where the punch head 203 is mounted to the punch driver 205 should be adjusted accurately so that the insufficient revolving of blade member 207 due to the cutting and protruding of the protrusion 221 does not occur. Namely, it is troublesome to adjust the mounting position of the punch head 203.
Furthermore, since the blade member 207 is revolved about the pin 209 in the horizontal direction by the protruded portion 217 at the lower end of the punch driver 205 which moves up and down, a contact portion between the protruded portion 217 and the blade member 207 is gradually inclined, and a component of force for revolving the blade member 207 in the horizontal direction becomes weak gradually. As a result, there arises a problem when the protrusion 221 is cut and protruded and the forming accuracy of the protrusion 221 is improved.